One type of vessel has a turret rotatably mounted on the vessel hull, so the turret does not rotate with the hull. A mooring structure such as several catenary lines extending up from the sea floor, connect to the turret, so mooring forces that limit vessel drift are transmitted through the turret to the vessel. A conduit with several hoses may extend from the sea floor up to the nonrotating turret, and through a fluid swivel structure at the top of the turret to pipes on the vessel.
A typical prior art turret is supported on the vessel by upper and lower bearings to withstand both the constant vertical load on the turret due to the weight of the mooring lines, and to withstand large net horizontal mooring forces applied during storms. One problem arising with such a system is that the upper and lower bearings have to be mounted and maintained precisely concentric on the vessel hull, which is very difficult to achieve. Even when concentricity is achieved, it can be lost by deformations of the ship hull. Still another problem is that the lower bearing is difficult to maintain and repair in the field. While the upper bearing lies above the sea surface, the lower bearing lies a considerable distance such as twenty meters below the sea surface, where it is difficult to replace large parts. It is possible to use a single upper bearing, but it is difficult to transfer large horizontal mooring load components to such a single upper bearing, without large internal loading of the turret and the use of a massive upper bearing. A mooring system for a turreted vessel which simplified bearing installation, maintenance and repair, would be of considerable value.